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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Debate about Cambrian lophotrochozoans ： ウィキペディア英語版 Debate about Cambrian lophotrochozoans Since 1990 there has been intense debate among paleontologists about the evolution in the Early Cambrian period of the "super-phylum" Lophotrochozoa, which is thought to include the modern molluscs, annelid worms and brachiopods, as well as their evolutionary "aunts" and "cousins". ==Organisms featured in the debate== The name "halwaxiid" was formed by combining the names of two members of the proposed group, ''Halkieria'' and ''Wiwaxia''. The group was defined as a set of Early to Mid Cambrian animals that had: a "chain mail" coat of three concentric bands of small armor plates that are called sclerites; in some cases, a small cap-like shell at the front end and in some cases both ends.〔 Some scientists are unhappy with this loose definition, arguing that such traits may have arisen convergently rather being inherited from a common ancestor. This objection suggests that the group is not monophyletic, in other words that the group does not contain all and only the descendants of a single common ancestor. In fact the originators of the term "halwaxiid" prefer an evolutionary "family tree" in which the halwaxiids are not monophyletic.〔 Other fossil organisms became involved in the debate as there were plausible arguments for considering them closely related to the halkieriids or ''Wiwaxia'' or both. One was the more recently discovered ''Orthrozanclus'', which looked an intermediate between the halkieriids and ''Wiwaxia'' as it had a shell like that of halkieriids, and unmineralized sclerites and long spines like those of ''Wiwaxia'' – in fact the article which first described ''Orthrozanclus'' introduced the term "halwaxiid".〔 New finds of ''Odontogriphus'' put this animal into play as well since, despite its lack of sclerites or shells, its feeding apparatus looks very like ''Wiwaxia''’s.〔〔 The siphogonotuchids, a very Early Cambrian group known only from isolated sclerites among the small shelly fossils, also appear in analyses as their sclerites suggest this group may have been close to the ancestors of halkieriids.〔〔The original, possibly incomplete, list includes ''Australohalkieria, Drepanochites, Eohalobia, Halkieria, Lomasulcachites, Ninella, Ocruranus, Oikozetetes, Orthrozanclus, Sinosachites, Siphogonuchites, Thambetolepis'', and ''Wiwaxia'' — 〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Debate about Cambrian lophotrochozoans」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.